Charcot-Marie-Tooth Polyneuropathy Syndrome (CMT) is the most common inherited neuropathy in humans. CMT type 1 is characterized clinically by slowly progressive distal muscle atrophy and weakness, electrophysiologically by decreased motor nerve conduction velocities, neuropathologically by a demyelinating hypertrophic neuropathy and "onion bulb" formation, and genetically by autosomal dominant segregation of the disease phenotype with most families demonstrating linkage to proximal 17p markers (CMT1A). CMT1A was recently demonstrated to be linked and associated with a large DNA duplication in 17p11.2p12. An animal model for CMT is the Trembler mouse (Tr dominant, TrJ semidominant) which presents similar clinical, electrophysiological, and neuropathological features. The Tr phenotype maps to mouse chromosome 11 in a region syntenic to the proximal region of human 17p; further, a peripheral nerve-specific gene (PMP-22) maps to the appropriate region of mouse chromosome 11 and is mutated in Tr. Preliminary experimental results suggest that the human homologue of the PMP-22 gene maps within the CMT1A duplication. The objective of this proposal is to obtain a complete molecular characterization of the CMT1A duplication region. This includes determining the size of the duplication and identifying the junction of the duplication through physical mapping of the CMT1A region; identifying expressed sequences within the duplication through the construction and screening of cDNA libraries from various human tissues; and determining the frequency of the duplication in CMT patients by means of Southern, pulsed field gel, and polymorphic (GT)n repeat analyses. Investigation of alternative mechanisms for CMT will include mutational analysis of the human PMP-22 gene in non-duplication CMT patients and molecular DNA analysis in partial trisomy 17p patients. The proposed work will lead to a DNA based diagnostic test for the duplication form of CMT and may lead to fundamental understanding of the molecular genetics and neurobiology of some inherited neuropathies. This understanding may elucidate options for therapeutic intervention for some forms of CMT.